Information technology (“IT”) organizations often employ a Wide Area Network (“WAN”) to, inter alia, deploy their processing infrastructures over a broad geographical area to increase productivity, support global collaboration, and minimize costs. Traditional local area network (“LAN”)-oriented infrastructures are generally insufficient to support global collaboration with high application performance and low costs. Deploying applications over WANs inevitably incurs performance degradation owing to the intrinsic nature of WANs, including such issues as operation over long distances, high latency, and high packet loss rate.
Transmission Control Protocol (“TCP”) is the software process that provides a communication service between an application program and the IP. Although TCP is the de facto standard for Internet-based commercial communication networks, it performs poorly under conditions of moderate to high packet loss and end-to-end latency. For instance, TCP generally exhibits substantial transmission inefficiencies during the “slow-start” phase.
More specifically, slow-start is used in conjunction with other algorithms to avoid sending more data than the network is capable of transmitting, that is, to avoid causing network congestion. It is also known as the exponential growth phase. During the exponential growth phase, slow-start works by increasing the TCP congestion window each time the acknowledgment is received, i.e., it increases the window size by the number of segments acknowledged. This happens until either an acknowledgment is not received for some segment or a predetermined threshold value is reached. If a loss event occurs, TCP assumes that it is due to network congestion and takes steps to reduce the offered load on the network. Once a loss event has occurred or the threshold has been reached, TCP enters the linear growth (congestion avoidance) phase. At this point, the window is increased by 1 segment for each RTT. This also happens until a loss event occurs.
Although the strategy is referred to as “slow-start”, its congestion window growth is quite aggressive. Nevertheless, the performance of the TCP slow-start phase generally degrades under conditions of long communication distances and high end-to-end latency, which generally are inherent characteristics of WANs. Accordingly, there exists a need to provide more efficient operation of TCP, especially during the slow-start phase.